If things had gone differently in Prague, the newcomer Makemake would now be considered in the same broad class as Earth or Jupiter, becoming the thirteenth planet of the solar system to be named.

At that meeting, the IAU started with a draft definition that included anything big enough for gravity to pull it into a roughly rounded shape, meaning that Pluto and similar largeish icy objects such as Makemake would have qualified. But the debate was eventually won by another camp, who argued that Pluto and its kind just formed a swarm of small debris that had never coalesced into planets proper. So today the solar system only has eight official planets, plus some dwarfs.

There are many astronomers and others who object to the IAU's decision in Prague, and would prefer to return to a definition that includes Pluto and probably all the other dwarf planets too. It is possible that they will get their way, changing the official definition at some future meeting of the IAU.

If that were to happen today, the thirteen named planets of the solar system would include Ceres, Eris and now Makemake. (I'm also counting the twin planet of Pluto-Charon as two. Although moons in general were sensibly excluded from planet status by the IAU's draft definition, Pluto's companion Charon was due to become half of a twin planet, for slightly technical reasons. It is not at present a dwarf planet; merely a moon.)

Perhaps there's no harm in having thirteen planets. Even the superstitious would soon be soothed, as astronomers will keep discovering more Pluto-like objects in the outer solar system. Eventually, we would probably have scores of planets.

It might be a problem, however, if you want to learn all their names and remember their order from the Sun.

Tuesday, August 14, 2007

Walking on Pluto

Where on Earth would you go to find a Pluto-like environment? The cold, dry Qaidam basin in north-west Tibet has been touted as the best place on Earth to find microbes similar to those that may have lived on Mars in the past, and the Apollo astronauts travelled to Mauna Kea, a 4200-metre-high dormant volcano on the Big Island of Hawaii, US, to test out their Moon buggies (though I'm told it didn't prove an especially useful exercise when they later got to the Moon).

But has anyone thought about Pluto? My friend Henry Throop, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, US, has for one. That's because producers of a new series on The History Channel called The Universe wanted to interview him on camera in a Pluto-like setting, since Henry is a member of NASA's New Horizons mission to the distant world.

"I suggested we fly to Siberia in the winter, where it's dark, cold, flat and icy," he says. But that plan didn't fly, for a very down-to-Earth reason: "They said that was going to max out their production budget," Henry explains. Instead, he suggested a trip to nearby Rocky Mountain National Park in the middle of the night. They went, and at 3 a.m. a team filmed Henry walking around on snowfields wearing a headlamp. US viewers got the chance to watch the one-hour episode on Tuesday 14 August.

What other places on Earth would be good analogues for planets (or dwarf planets)?

Monday, July 09, 2007

Pluto to get a coin?

Astronomers may have demoted Pluto from the ranks of full-fledged planets, but that won't stop the US from issuing a commemorative silver $1 coin for Pluto along with those for the eight astronomically correct planets, at least if Texas Representative Sheila Jackson-Lee has her way.

But these coins aren't likely to get much use at the corner store. The bill specifies them as legal tender, but unlike the usual pocket change, they're to be made from real silver and would be sold for a $10 premium per coin.

They're aimed at coin collectors, and the bill specifies that any profits would be split among the NASA Family Assistance Fund, which provides money to the families of NASA personnel who die while performing their jobs; the Dr. Ronald E. McNair Educational Science Literacy Foundation; the Dorothy Jemison Foundation for Excellence, which also promotes scientific literacy; and the Smithsonian's National Air and Space Museum. The bill also calls for minting a smaller number of $50 gold pieces bearing an image of the Sun.

Pluto was demoted after the previous bill was introduced, but the new version stays with nine planets. The proposed bill calls for nine different coins, each bearing on the front "an image of 1 of the 9 planets of the solar system, including Earth". The back of the Pluto coins are to have a design on the back "emblematic of telescopic exploration of deep space", and the search for Earth-like planets around other stars.

But the politicians did make one small, symbolic step toward astronomical correctness. What had been called the "Pluto coin" in the previous version is now called the "Pluto (and other dwarf planets) coin".

If the coins do come out, would you buy any? Do you think they should have left Pluto off the list, or added any other celestial bodies?

With lectures for students to be held throughout the day on Friday in the town's high school auditorium, the real fun is likely to take place on Saturday, when there is going to be a "Big Dipper" ice cream social at the Weber House and Gardens (pictured) and a concert in the park featuring, among other acts, Haley Crouch & The Comet Blues Band (whose song "Bring Pluto Back" can be heard on the Expo's website).

If you're wondering why this geeky extravaganza would be held in Streator, the answer is simple: it is the hometown of Clyde Tombaugh, who was born there in 1906.

Who do you think will take a stand on Pluto next? Are there any other municipalities with major or minor (or dwarf?) connections to Tombaugh left?